This isn't just your typical 'aliens from outer space' film. It is a more subtle telling of creatures who you don't see on screen until halfway into the movie, though you know they're out there, lurking, watching. When they will strike next? No one knows.
Alien life forms start growing in Northern Mexico after a NASA plane crashes, and these life forms grow to monstrous proportions (looking exactly like flying Octupuses!). They start taking over the area, which has been quarantined by both the Mexican and U.S. governments. In fact, the Americans have built a massively huge wall at the border to keep these aliens out.
Andrew, an American journalist, is hired by his boss to escort his daughter back to the U.S. Unfortunately, they miss the last boat back to the U.S. and hire some dodgy-looking Mexicans to escort them through the Quarantine zone. What will they encounter during their trip? Will they make it out alive? Will they fall in love even though she is engaged?
The alien monsters are very briefly shown in the beginning of the film. Midway through they come into focus, albiet briefly, but it is not until the very end of the film that you actually see these creatures in a scene that is both poignant and touching (and a bit confusing). And then the film ends.
Monsters is a good escapist film. The acting is OK, the plot is a little far-fetched, and the ending leaves you hanging. But it's a perfect escape from all the Christmas craziness.